1. Field of the Invention
This invention relates to a process for the production of crude shale oil, hydrocarbon gas, carbon oxide gas and hydrogen suitable for use as a feed stock for refineries, and more particularly, it relates to a process wherein particulate oil shale is retorted to produce crude shale oil, hydrocarbon gas, carbon oxide gas and hydrogen.
2. Description of the Prior Art
Prior art attempts to develop economic processes for utilizing oil shale have followed numerous different paths as disclosed in the following U.S. Pat. Nos.: 2,434,815, 2,901,402, 3,503,869, 3,777,940, 2,560,767, 2,982,701, 3,561,927, 3,803,022, 2,694,037, 3,349,022, 3,663,421, 3,841,992, 2,813,823, 3,384,569, 3,736,247, 3,887,453, 2,832,725, 3,475,319, 3,743,697, 3,939,057.
One such path comprises in situ retorting wherein the shale is burned in place and the heat produced is utilized to decompose the surrounding shale. That process has not been completely satisfactory because the impermeability of the shale prevents movement of gases required for combustion and the recovery of products.
Another path involves direct combustion retorting wherein crushed shale is heated by combustion occurring in the retort by burning injected fuels and/or the residual carbon remaining on the retorted shale with air. Commonly, this is done in a vertical vessel into the top of which fresh shale is fed continuously or batchwise and spent shale is removed from the bottom. The direct combustion retorting process occurs within the vessel in four zones known as: (1) a shale preheating zone forming the upper part of the retort vessel wherein raw particulate shale is introduced and brought up to retorting temperature by direct heat exchange with a heat yielding fluid; (2) a retorting zone wherein the kerogen component of the shale is decomposed to shale vapors and gas; (3) a combustion zone wherein controlled combustion of the available combustible material with air is effected to provide at least a portion of the heat energy required in the retorting operation; and (4) a shale cooling zone wherein the spent shale particles are cooled to a desired low temperature suitable for handling while preheating at least a portion of the recycle gases separated from the shale decomposition products of the retorting operation. Air for combustion is forced into the combustion zone. The hot gases, both combustion and recycle, pass up through the shale causing the kerogen to decompose. The product then is removed as a vapor out the top and condensed.
Equally common are down draft designs wherein the shale is fed upwardly and combustion occurs in the top and product is removed from the bottom. These designs have the advantage of good heat efficiency but disadvantages in that the product is diluted with the combustion gases making recovery of light hydrocarbons difficult and presenting environmental pollution problems relating to disposal of the byproducts of the combustion zone. Also, since the shale contains large amounts of calcite and dolomite which decompose endothermally at 1050-1100.degree. F, temperature control is very critical and difficult in the combustion zone.
Another system of retorting involves indirect heating of the shale using ceramic balls to convey the heat. The spent shale is burned in a separate vessel to supply the heat to raise the temperature of the balls to such a point that when they are mixed with the shale in a retort, the shale is heated to retorting temperatures. The spent shale and the balls then are separated and the ceramic balls are recycled. This process has the advantage that the light gases produced are not diluted with the combustion products. The disadvantages are largely mechanical due to the difficulties of designing the necessary equipment.
Many other processes have been reported, but they essentially operate as variations of those described above and have yet to provide an economic means of retorting the oil shale.